| Linear concentrating solar collector is the main technique in the area ofmedium-high temperature solar thermal utilization. While parabolic trough solarcollector (PTC) is widely applied in solar thermal power generation, solar airconditioner and refrigeration, solar-powered seawater desalination, solar hydrogenproduction in medium temperature and other fields because of relatively high thermaland advantage of cost in scale utilization. However, in actual application, it usuallyneeds several energy conversion steps from heat collection (solar energy thermalconversion) to heat application, the heat loss can not be avoided in each step. Torealize high efficiency in heat collection and application, heat loss in each step shallbe reduced as much as possible. In addition, the initial invented cost must beconsidered. Therefore, in order to realize low cost and high efficiency in heatcollection and application, many key issues of PTC system in concentrator, absorber,tracking controller, arrangement and so on need to be resolved. This thesis is mainlydevoted to research on the key issue that how to improve the thermal conversion andapplication efficiency of PTC system. The main works are includes the followingaspects:(1) The basic theory and related technology about the solar energy thermalconversion process of PTC were summarized; a type of all-glass insulation evacuatedabsorber tube with inserted receiving tube was designed, its thermal performance wastheoretically analyzed and experimentally tested. The test result showed that thethermal efficiency of this tube was equal to90～93%of that in glass-metal evacuatedtube, and equal to that with cavity absorber.(2) A method to calculate the energy flux density distribution of focal line ofPTC is presented, and the energy flux density distribution on the surfaces ofcylindrical receiver, V shaped cavity receiver and plane receiver of PTC werecalculated with software of Origin. According to the energy flux density distributionand the use of the structure type of receiver, the structure design optimization of PTCsystem was researched and analyzed.(3) The theoretical analysis and experimental research on the cosine loss effectand end loss effect of PTC were carried out. The general theoretical model of end losseffect and cosine loss effect of PTC with arbitrary orientation, arbitrary tilt angle wasbuilt; the methods to reduce or compensate the end loss effect by extending heatabsorber tube and setting an end plane mirror at one end of PTC were presented, theapplication condition of different methods was analyzed and discussed, and the feasibility of these methods was tested; the theoretical model of optical efficiency ofPTC with arbitrary direction and arbitrary tilt angle was built, and the best orientationand tilt angle range were given by analyzing and testing the theoretical calculation.(4) The analysis and research were carried out on related issues of trackingmode, tracking control and design of PTC system with one-dimensional tracking. Atracking control system with rapid-rough and slow-accurate tracking mode wasdesigned. An indirect tracking precision measurement method was presented and atest on the tracking precision was carried out. The experimental research of theinfluence of pointing deviation on heat collecting efficiency was carried out. It showsthat when the deviation of PTC is within0.40°, the change of its thermal efficiency isnot big. The correct way was given to fix solar location sensor for adopting trackingcontrol mode of photoelectric sensor. The research on the influence of rotation angleprocess (maximum rotation angle of axis) on heat collecting of PTC in a day wascarried out.(5) The shading geometric model and arrangement of PTC array were analyzedand researched based on priciples of geometrical optics. Aim at one-dimensionaltracking PTC array, the shading model of PTC array with arbitrary orientation wasbuilt. Based on comprehensive considering the daily change of solar beam radiationand the use rate of sunlight field, and by theoretical calculation, the reference value ofminimum installation space (space between adjacent PTC units) of PTC array withdifferent orientation was given. The results show that for PTC array consiting ofcollector unit with aperture w=3m and length L=20m, the minimum installationspace of arbitrary orientation PTC array may be between4.5m and5.0m in the siteof latitude φ=25.01°.(6) The experimental research on the performance of single-effect lithiumbromide absorption refrigeration system powered by PTC was carried out. Thethermal efficiency of PTC and refrigeration coefficient of single-effect lithiumbromide absorption chiller were mainly tested. When the system is under heatingmodel, the thermal performance was tested and analyzed. Regarding existingproblems and shortcomings of the whole system, the structure optimization analysiswas conducted to seek for solutions to realize high efficiency thermal collection andapplication. The research results showed that：when the solar beam radiation is rangefrom0.40to0.90kW/m2, the instantaneous thermal efficiency of the PTC system isbetween0.42and0.55, and the instantaneous power is between9kW and21kW; theaverage refrigeration coefficient of chiller is between0.18and0.60, and refrigerationCOP is around between0.12and0.27. |
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